From: Felipe Balbi <balbi@kernel.org>
To: Anurag Kumar Vulisha <anuragku@xilinx.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "linux-usb\@vger.kernel.org" <linux-usb@vger.kernel.org>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"v.anuragkumar\@gmail.com" <v.anuragkumar@gmail.com>
Subject: RE: [PATCH] usb: dwc3: gadget: Correct the logic for finding last SG entry
Date: Fri, 07 Jun 2019 09:49:59 +0300 [thread overview]
Message-ID: <87ftoldh48.fsf@linux.intel.com> (raw)
In-Reply-To: <BYAPR02MB559181C009B74446A797838DA7170@BYAPR02MB5591.namprd02.prod.outlook.com>
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Hi,
Anurag Kumar Vulisha <anuragku@xilinx.com> writes:
>>> The dma_map_sg() merges sg1 & sg2 memory regions into sg1-
>>>dma_address.
>>> Similarly sg3 & sg4 into sg2->dma_address, sg5 & sg6 into the
>>> sg3->dma_address and sg6 & sg8 into sg4->dma_address. Here the
>>memory
>>> regions are merged but the page_link properties like SG_END are not
>>> retained into the merged sgs.
>>
>>isn't this a bug in the scatterlist mapping code? Why doesn't it keep
>>SG_END?
>>
>
> Thanks for providing your comment.
>
> I don't think it is a bug, instead I feel some enhancement needs to be done in
> dma-mapping code.
>
> SG_END represents the last sg entry in the sglist and it is correctly getting
> set to the last sg entry.
>
> The issue happens only when 2 or more sg entry pages are merged into
> contiguous dma-able address and sg_is_last() is used to find the last sg entry
> with valid dma address.
Right, and that's something that's bound to happen. I'm arguing that, perhaps,
dma API should move SG_END in case entries are merged.
> I think that along with sg_is_last() a new flag (SG_DMA_END) and function
> (something like sg_dma_is_last() ) needs to be added into dma-mapping code for
> identifying the last valid sg entry with valid dma address. So that we can
> make use of that function instead of sg_is_last().
Sure, propose a patch to DMA API.
--
balbi
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next prev parent reply other threads:[~2019-06-07 6:50 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-29 14:59 [PATCH] usb: dwc3: gadget: Correct the logic for finding last SG entry Anurag Kumar Vulisha
2019-06-05 8:03 ` Felipe Balbi
2019-06-06 15:32 ` Anurag Kumar Vulisha
2019-06-07 6:49 ` Felipe Balbi [this message]
2019-10-23 16:58 ` Jack Pham
2019-10-25 12:01 ` Anurag Kumar Vulisha
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